Corrosion-responsive coating formulations for protection of metal surfaces

ABSTRACT

Methods and compositions are described for protecting a metal surface against corrosion. The method involves applying to the metal surface a coating formulation that comprises a radiation curable resin and a corrosion-responsive agent that is capable of releasing a corrosion-inhibiting ion in response to exposure to ionic species characteristic of those present on a metal surface undergoing oxidative corrosion; and exposing the coating formulation to radiation whereby the radiation curable resin forms a corrosion-resisting coating having a low spontaneous release rate of the corrosion-responsive agent into the environment.

CROSS REFERENCE TO RELATED PATENTS AND PATENT APPLICATIONS

[0001] The present application claims priority to U.S. ProvisionalPatent Application Serial No. 60/386,058, filed Jun. 4, 2002, and to theU.S. Provisional Application Serial No. 60/466,298, filed Apr. 29, 2003,each of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] (1) Field of the Invention

[0003] The present invention relates to coatings for metal surfaces thatprotect the surfaces from corrosion, and more particularly to radiationcurable corrosion-responsive coatings for metals and components of suchcoatings.

[0004] (2) Description of the Related Art

[0005] In the United States approximately $300 billion per year indirect costs is lost due to metallic corrosion. More than one third ofcosts are considered avoidable using existing know-how and technology.Coatings are the primary and most economical means for controlling thecorrosion of metals. The key factors that influence corrosion are thetype of metal being used (aluminum, steel, copper, etc.) and theenvironment to which the metal is exposed (pH, temperature, humidity,chemicals, etc.).

[0006] Current strategies for corrosion protection include: dispersionof pigments in coating systems which act as passivating agents,including strontium chromate, zinc chromate, zinc phosphate, bariummetaborate, etc.; dispersion of pigments in coating systems whichprovide cathodic protection (e.g., zinc dust which acts as a sacrificialanode); and the provision of mechanical protection by applying thickmultilayer coating systems such as epoxies, urethanes, acrylics andrubbers, which are impervious to moisture and chemical ingress. What islacking with current coating strategies, however, is an environmentallyfriendly coating system that prevents corrosion and pitting even in thepresence of pinholes or scratches.

[0007] Problems with a passivation coating, such as chromium VI (theform of chromium commonly used in aerospace coatings), include the factthat chromium is a carcinogen and federal, state and local agencies haveissued regulations that limit or prohibit the use of chromatedmaterials. OSHA regulates the amount of hexavalent chromium to whichworkers can be exposed, and has proposed reducing the PermissibleExposure Limit (PEL) from the current 50 micrograms/m³ to less than 1microgram/m³. OSHA's proposed PEL would severely impact the use ofhexavalent chromium throughout the aerospace sector.

[0008] The primary function of barrier coatings is to prevent theingress of water and salts. However, such coatings often lack pinholeprotection. Any pitting or scarring that penetrates the underlyingstructures can lead to catastrophic corrosion damage. To compensate forthe lack of pinhole protection, multiple layers are applied.

[0009] Sacrificial coatings are designed to corrode and cathodicallyprotect the underlying structure. These coatings wear more readily, andthe layer thickness and its associated weight can negatively impactstructural design.

[0010] Epoxy primers containing chromate with polyurethane top coats arewidely used for corrosion protection in the aircraft industry. Strontiumchromate coatings, while extremely effective, are under significantpressure to be eliminated because of their carcinogenic classification.In addition, chromic acid anodizing and other chromium conversioncoating systems are also commonly employed to enhance corrosionprotection and also adhesion of the epoxy primer coating to aluminum.

[0011] The need for anti-corrosion coatings, which are pinhole andscratch tolerant, coupled with growing environmental concerns involvingheavy metals, such as hexavalent chromium, has led to new coatingstrategies. In one area, coatings that employ intrinsically conductivepolymers (ICPs) have been reported. The first documented observations ofcorrosion protection of steel by polyaniline were reported in 1981 byMengoli, et al., Appl Polymer Sci., 26:4247 (1981). Since then, numerouspapers have been published on the corrosion protection of carbon steel(Kinlen, et al., Corrision, 58:490(2002)), stainless steel (Casparac etal, J. Electrodhem. Soc., 148:B138 (2001)), iron (Beck,Metalloberflacche, 46:177 (1992); and Beck, et al., Electrochimica Acta,39:229 (1994)), titanium, copper (Brusic, et al., J. Electrochem. Soc.,144:436 (1997), and aluminum alloys (Gelling, et al., Prog. OrganicCoatings, 43:149 (2001)), with ICP's. Two comprehensive review articleshave been published. See, e.g., McAndrew, Trends in Polymer Science, 5:7(1997); and Spinks, et al., J. Solid State Electrochemistry, 6:85(2002).

[0012] Other work has led to the use of “smart” coatings, which containmaterials designed to release a corrosion-inhibiting species on demandduring corrosion. For example, in WO 90/10095, Wallace reports a polymercoating, where the polymer is preferably an electrically conductiveoligomer, such as polypyrrole, that contains ions such as chromate,EDTA, and others, which are released in response to contact with ionicspecies that are the product of the oxidative/reductive chemicalreactions that occur during corrosion. In U.S. Patent Publication2002/0197468A1, Sinko identifies corrosion-inhibiting organic pigments,such as 2,5-dimercapto-1,3,4-thiadiazole (DMTD), and others, thatdemonstrate “throw power” (an ability to maintain a scribed line on acoated metal surface free of corrosion in a corrosive environment). InU.S. Pat. No. 6,139,610, Sinko describes certain inorganic and organicpigment compositions as being effective corrosion inhibitors, again withDMTD being mentioned. In another publication, Sinko identified certaininorganic materials as being potential replacements for chromates.Sinko, J., Prog.in Org. Coatings, 42:267-282 (2001).

[0013] Although epoxy-based coatings predominate in commercial corrosionprevention applications, other polymeric systems are suggested. Onedrawback of many polymeric systems, however, is the use of solvents, orthe formation of water or gas during curing. The removal of thesolvents, water, or gas from the coating as it cures leaves holes, pits,and voids in the cured film, through which water, oxygen and othercorrosive elements can penetrate to reach the metal surface.

[0014] Radiation-curable polymer systems, such as UV-curable resins, canbe formulated to be solvent-free, and have been used to form films thatcontain various chemicals. Kim, Y-B, et al., Polymers for AdvancedTechnologies, 13(7):522-526 (2002), have reported UV cured transparentfilms containing conductive microgels coated withpolyaminiline/dodecylbenzenesulphonic acid (DBSA). Others have reportedthe corrosion-protective effects for aluminum of polymeric blendcoatings containing either polyaniline, polypyrrole, or other polymers,and UV-curable urethane acrylate binders. Vang, C. et al., PolymerPreprints, 43(1), Spring 2002, Papers presented at the ACS meeting heldOrlando, Fla., Apr. 7-11, 2002, ACS Div. of Polymer Chemistry. InJapanese unexamined patent JP 11/172103, aniline-type resin compositionsare cured with UV radiation. The polyaniline in the cured films is dopedwith a sulphone compound, and the film is reportedly useful as anantistatic agent.

[0015] Despite the availability of radiation-cured polymeric systems,they have not been widely used to form corrosion-resisting coatings, andcertain problems remain to be resolved. It is known, for example, thatthe corrosion-inhibiting compound DMTD is itself a strong UV absorber.It is unclear, therefore, whether such a material could be included as acomponent in a UV-cured resin system at a level that would be useful forcorrosion inhibition without interfering with the curing of the coating.

[0016] Accordingly, therefore, it would be useful to providecorrosion-inhibiting methods and compositions that provided effectivecorrosion protection for metal surfaces. It would also be useful if suchmethods and compositions supplied corrosion-inhibiting agents inresponse to actual corrosion on a metal surface, and if they providedcorrosion protection for pinholes and scratches that might occur on themetal surfaces. It would also be useful if such methods and compositionsretained their effectiveness through normal weather exposure.

SUMMARY OF THE INVENTION

[0017] Briefly, therefore the present invention is directed to a novelmethod of protecting a metal surface against corrosion, the methodcomprising:

[0018] applying to the metal surface a coating formulation thatcomprises a radiation curable resin and a corrosion-responsive agentthat is capable of releasing a corrosion-inhibiting ion in response toexposure to electrochemical conditions characteristic of those presenton a metal surface undergoing oxidative corrosion; and

[0019] exposing the coating formulation to radiation whereby theradiation curable resin forms a corrosion-resisting coating having a lowspontaneous release rate of the corrosion-responsive agent into theenvironment.

[0020] The present invention is also directed to a novel anti-corrosioncoating formulation comprising a radiation curable resin and acorrosion-responsive agent that is capable of releasing acorrosion-inhibiting ion in response to exposure to electrochemicalconditions characteristic of those present on a metal surface undergoingoxidative corrosion.

[0021] The present invention is also directed to a novel corrosionresisting coating for a metal surface, the coating comprising acorrosion-responsive agent dispersed in a radiation cured crosslinkedpolymer matrix.

[0022] The present invention is also directed to a novel metal surfaceprotected against corrosion comprising:

[0023] a metal surface; to which is adhered,

[0024] a radiation-cured polymer matrix that has been formed accordingto any one of the methods described herein.

[0025] The present invention is also directed to a novel method ofproducing an intrinsically conductive polymer salt of acorrosion-responsive agent, the method comprising:

[0026] subjecting a liquid mixture containing a corrosion-responsiveagent to high-shear mixing to separate the corrosion-responsive agentinto very fine particles;

[0027] adding a monomer of an intrinsically conductive polymer to themixture of fine corrosion-responsive agent particles while subjectingthe mixture to high-shear mixing;

[0028] adding an oxidant to the mixture to facilitate polymerization ofthe monomer of the intrinsically conductive polymer into anintrinsically conductive polymer which is doped by thecorrosion-responsive agent to form the ICP/CRA salt; and

[0029] recovering the ICP/CRA salt.

[0030] Among the several advantages found to be achieved by the presentinvention, therefore, may be noted the provision of corrosion-inhibitingmethods and compositions that provided effective corrosion protectionfor metal surfaces; and also the provision of such methods andcompositions that supply corrosion-inhibiting agents in response toactual corrosion on a metal surface; and also the provision of suchmethods and compositions that provide corrosion protection for pinholesand scratches that might occur on the metal surfaces; and also theprovision of such methods and compositions that retain theireffectiveness through normal weather exposure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 shows differential refractive index (DRI) chromatograms fora polyaniline standard and a soluble fraction of polymerized2,5-dimercapto-1,3,4-thiadiazole (poly-DMcT);

[0032]FIG. 2 shows an overlay the DRI curves for the two homopolymerstandards shown in FIG. 1 with the corresponding curves for two separatesamples of 2,5-dimercapto-1,3,4-thiadiazole salt of polyaniline(Pani-DMcT) labeled #1 and #2, and which indicates the presence ofpoly-DMcT, as well as the presence of polyaniline in each sample ofPani-DMcT;

[0033]FIG. 3 is a retention time expansion of the polymer region of thechromatograms shown in FIG. 2, and shows components eluting withretention times earlier than the polyaniline standard, which suggestsmultiple species, possibly pure polyaniline and copolymers of anilineand DMcT, and also indicating poly-DMcT in the Pani-DMcT samples #1 and#2; and

[0034]FIG. 4 is a normalized difference plot for Pani-DMcT vs. apolyaniline standard, which reveals that Pani-DMcT #1 contains lesspoly-DMcT relative to its earlier eluting components than in the case ofPani-DMcT #2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] In accordance with the present invention, it has been discoveredthat metal surfaces that are subject to environmental corrosion, inparticular to oxidative corrosion, can be protected against suchcorrosion by applying to the metal surface a coating formulation thatcomprises a radiation curable resin and a corrosion-responsive agent.The corrosion-responsive agent, which is described in detail below, is acompound that is capable of releasing a corrosion-inhibiting ion inresponse to exposure to electrochemical (oxidation/reduction) conditionscharacteristic of those present on a metal surface undergoing oxidativecorrosion. After the coating formulation is applied to the metalsurface, it is exposed to radiation in a manner that causes theradiation curable resin to form a corrosion-resisting coating having alow spontaneous release rate of the corrosion-responsive agent into theenvironment.

[0036] In a particularly useful embodiment, it has been found that somecorrosion-responsive agents oxidatively dimerize or polymerize under thesame conditions as are used to cure the resin to form homodimers,homopolymers, or copolymers with a component of the radiation curableresin. These dimerized or polymerized agents reductively depolymerizeunder corrosion conditions to release corrosion-inhibiting ions.Coatings formed with these types of agents are exceptionally weatherableand surprisingly effective for corrosion inhibition.

[0037] The novel method offers several advantages over anti-corrosioncoatings of the prior art. The present compositions provide usefulamounts of corrosion-inhibiting ions, or compounds that can form suchions, and act as reservoirs of corrosion-inhibiting ions. Thecompositions permit the formation of “smart” coatings, in that theyrelease corrosion-inhibiting ions in response to the presence ofelectrochemical conditions that are typical of the oxidative/reductiveconditions present on a metal surface when that surface is undergoingoxidative corrosion. Another advantage of the present method and presentcoatings is that the corrosion-inhibiting ions are not easily leachedout of the novel coatings by exposure of the coatings to normalenvironmental conditions, such as to rain, water immersion, or the like.In other words, they have a low spontaneous release rate of thecorrosion-inhibiting ions. The gives the present coatings a long servicelife, and permits their use in applications that require long outdoorexposure.

[0038] It is believed that a combination of two factors enable thepresent invention to release corrosion-inhibiting ions in response tocorrosion while maintaining a low spontaneous release rate for the ions.One factor is the formation of a coating wherein thecorrosion-inhibiting ions are supplied by a corrosion-responsive agent.

[0039] In the present invention, a “corrosion-responsive agent” is acompound that is capable of releasing a corrosion-inhibiting ion uponexposure to electrochemical (oxidation/reduction) conditionscharacteristic of those present on a metal surface undergoing oxidativecorrosion. As is well known to those skilled in the study of metalcorrosion, oxidative corrosion of a metal by contact with oxygen andwater causes the formation of an electrogalvanic cell that ischaracterized by the presence of metal cations, hydroxyl anions, and thelike. When the corrosion-responsive agent of the present invention is inoperative contact with such a corroding metal surface, it is believed toreact with one or more of the anions or cations that are a part of theoxidative corrosion electrogalvanic cell to produce acorrosion-inhibiting ion. Therefore, the corrosion-responsive agentitself undergoes oxidation or reduction in response to its exposure tothe corrosion. However, under non-corrosive conditions, thecorrosion-responsive agent remains unreacted and stable, and has a lowrate of spontaneous ionization to release a corrosion-inhibiting ion.

[0040] Another factor that enhances the benefits of thecorrosion-responsive agent in the present invention is the dispersion ofthe corrosion-responsive agent in a radiation curable coating. It isbelieved that the present radiation curable coating is a durable coatinghaving very low porosity, which acts as a barrier coating to thepenetration of water and oxygen to the metal surface and also modulates,or “throttles”, the movement of the corrosion-inhibiting ions that arereleased by the corrosion-responsive agent.

[0041] In the present invention the corrosion-inhibiting ion can be acorrosion-inhibiting cation or a corrosion-inhibiting anion.

[0042] When the corrosion-inhibiting ion is a cation, it can be aninorganic cation or an organic cation. Examples of inorganic cationsthat can act as the corrosion-inhibiting ion of the present inventioninclude ions selected from the group consisting of: Ca, Sr, Ti, Mo, Zr,Ce, and Fe. Examples of organic cations that can act as thecorrosion-inhibiting ion of the present invention include ions selectedfrom the group consisting of: ammonium, alkyl-ammonium, andcycloalkyl-ammonium.

[0043] When the corrosion-inhibiting ion is an anion, it can be aninorganic anion or an organic anion. Examples of inorganic cations thatcan act as the corrosion-inhibiting ion of the present invention includean anion that is selected from the group consisting of: CrO₄ ²⁻, CrO₁₂H₈⁵⁻, PO₄ ³⁻, HPO₄ ³⁻, MoO₄ ²⁻, BO₂ ²⁻, SiO₃ ²⁻, NCN²⁻, HPO₃ ²⁻, NO²⁻,P₃O₁₀ ⁵⁻; and CO₃ ²⁻. In preferred embodiments, the inorganiccorrosion-inhibiting anion can be selected from the group consisting of:PO₄ ³⁻, HPO₄ ³⁻, MoO₄ ²⁻, BO₂ ²⁻, SiO₃ ²⁻, NCN²⁻, and P₃O₁₀ ⁵⁻.

[0044] The corrosion-inhibiting anion of the present invention can be anorganic anion. In an embodiment, the organic corrosion-inhibiting anionis one that is formed by the ionization of a corrosion-responsive agentthat is selected from the group consisting of mercapto-substitutedorganics, thio-substituted organics, and dimers, trimers, oligomers, andpolymers thereof. Examples of useful mercapto-substituted organiccorrosion-responsive agents include a mercapto-substituted aryl orheteroaryl. A particularly useful mercapto-substituted organiccorrosion-inhibiting agent is 2,5-dimercapto-1,3,4-thiadiazole.

[0045] In another embodiment, the corrosion-inhibiting anion is one thatis formed by the ionization of a corrosion-responsive agent that isselected from the group consisting of:1-(4-hydroxyphenyl)-1H-tetrazol-5-thiol, 1,2,4-triazole-3-thiol,1-pyrollidinecarbodithioic acid, 2,2′-dithiobis(benzothiazole),2,4-dimercapto-6-amino-5-triazine, 2,4-dithiohydantoin,2,5-dimercapto-1,3,4-thiodiazole, 2,5-dimethylbenzothiazole,2-amino-1,3,4-thiadiazole, 2-mercapto-5-methylbenzimidazole,2-mercapto-5-nitrobenzimidazole, 2-mercaptobenzimidizole,2-mercaptobenzoxazole, 2-mercaptoethane sulfonic acid,

[0046] 2-mercaptoimidazole, 2-mercaptothiazoline, 2-thiouracil,3-amino-5-mercapto-1,2,4-triazole,5,5-dithio-bis(1,3,4-thiadiazole-2(3H)-thione,5-amino-1,3,4-thiadiazole, 6-amino-2-mercaptobenzothiazole,6-ethoxy-2-mercaptobenzothiazole, 6-mercaptopurine, -alky- orN-cycloalkyl-dithiocarbamates, alkyl- and cyclo-alkyl mercaptanes,benzothiazole, dimercapto pyridine, dimethyidithio carbamic acid,dithiocyanuric acid, mercaptobenzothiazole, mercaptobenzoxazole,mercaptoethanesulfonic acid, mercaptoimidazole, mercaptopyridine,mercaptopyrimidine, mercaptoquinoline, mercaptothiazole,mercaptothiazoline, mercaptotriazole, O,O-dialkyl- andO,O-dicycloalkyl-dithiophosphates, O-alkyl- orO-cycloalkyl-dithiocarbonates, o-ethylxanthic acid,quinoxaline-2,3-thiol, thioacetic acid, thiocresol, thiosalicylic acid,trithiocyanuric acid, and dimers, trimers, oligomers, and polymersthereof.

[0047] The organic corrosion-inhibiting agent can be an organicphosphonic acid or salt or ester.thereof. Organic phosphonic acids canbe mono-, di-, tri-, tetra-, or polyphosphonic acids. Phosphonic acidsthat are di-, tri-, tetra-, or poly-phosphonic acids (which may betermed “polyphosphonic acids herein) are preferred for use in thepresent invention. Other acidic groups, such as carboxylic, boric, andthe like, can also be present on the molecule in addition to thephosphonic acid groups. Polymers that have at least two pendentphosphonic acid groups, wherein each such pendent phosphonic acid groupis a mono-functional phosphonic acid group, are also included aspolyphosphonic acids.

[0048] A preferred form of phosphonic acids are aminoalkylphosphonicacids and hydroxyalkylphosphonic acids having the general formula:

R¹—(CH₂—(PO₃)M₂)_(x), or

R¹—((PO₃)M₂)_(x)

[0049] where:

[0050] M is selected from the group consisting of hydrogen, an alkalinemetal, alkyl, alkenyl, alkynyl, alkoxy, aryl, cyclic, heteroaryl, andheterocyclic;

[0051] R₁ is selected from the group consisting of amino, aminoalkyl,and hydroxyalkyl; and

[0052] x is a number equal to the valence of R¹, provided that x is 1 orhigher.

[0053] In a more preferred embodiment, x is 2 or higher.

[0054] Illustrative of some of the organic phosphonic acids that areuseful in the present invention are:n-octyldecylaminobismethylenephosphonic acid, dodecyldiphosphonic acid,ethylidenediaminotetramethylenephosphonic acid,hydroxyethylidenediphosphonic acid, 1-hydroxyethylidene1,1-diphosphonicacid, isopropenyldiphosphonic acid,N,N-dipropynoxymethylaminotrimethylphosphonic acid,oxyethylidenediphosphonic acid, 2-carboxyethylphosphonic acid,N,N-bis(ethynoxymethyl)aminomethyltriphosphonic acid,nitriletrimethylenephosphonic acid, aminotrimethylenephosphonic acid,diethylenetriaminepentakis(methylenephosphonic) acid,amino(trimethylenephosphonic acid), nitrilotris(methylenephosphonicacid), ethylenediaminotetra(methylenephosphonic acid),hexamethylenediaminetetra(methylenephosphonic acid),diethylenetriaminepenta(methlenephosphonic acid),glycine,N,N-bis(methylenephosphonic acid),bis(hexamethylenetriaminepenta(methylenephosphonic acid), and2-ethylhexylphosphonic acid.

[0055] Suitable organic phosphonates that are useful in the presentinvention also include alkali metal ethane 1-hydroxy diphosphonates(HEDP), alkylene poly(alkylene phosphonate), as well as aminophosphonate compounds, including amino aminotri(methylene phosphonicacid) (ATMP), nitrilo trimethylene phosphonates (NTP), ethylene diaminetetra methylene phosphonates, and diethylene triamine penta methylenephosphonates (DTPMP). The phosphonate compounds may be present either intheir acid form or as salts of different cations on some or all of theiracid functionalities. Preferred phosphonates to be used herein arediethylene triamine penta methylene phosphonate (DTPMP) and ethane1-hydroxy diphosphonate (HEDP). Such phosphonates are commerciallyavailable from Monsanto under the trade name DEQUEST®.

[0056] In an embodiment of the present invention thecorrosion-responsive agent is the salt of an intrinsically conductivepolymer and a corrosion-inhibiting anion that is selected from any ofthe corrosion-inhibiting anions described above.

[0057] The terms “intrinsically conductive polymer”, or “ICP”, as usedherein, are intended to include any polymer that, in at least onevalence state, has an electrical conductivity greater than about 10⁻⁸S/cm, and preferably greater than about 10⁻⁶ S/cm. ICP's generally havepolyconjugated nelectron systems and can be doped with an ionic dopantspecies to an electrically conductive state. A number of conjugatedorganic polymers that are suitable for this purpose are known in the artand include, for example, polyacetylene, polyaniline, polycarbazole,polyfuran, polyisothionaphene, polyparaphenylene, polyparaphenylenesulfide, polyparaphenylene vinylene, polyperinaphthalene,polyphthalocyanine, polypyrrole, polyquinoline, andpolythiophenepolyheteroarylenevinylene, in which the heteroarylene groupis thiophene, furan or pyrrole. Mixtures of such ICPs can also be used.

[0058] It is known that ICP's, and specifically polyaniline,polythiophene, and polypyrrole, may be made electrically conductiveeither by electrochemical or chemical polymerization of protonatedmononers, or by protonation of the neutral polymer by exposure toprotonic acids (often called dopants). For example, polyaniline that iselectrically conductive in its doped, or salt, form typically has aconductivity of greater than about 10⁻⁸ S/cm. However, in its neutral,or base form, it is non-conductive and has a conductivity of less thanabout 10⁻⁸ S/cm.

[0059] In general, polyanilines suitable for use in this invention arehomopolymers and copolymers derived from the polymerization ofunsubstituted or substituted anilines of Formula I:

[0060] wherein:

[0061] n is an integer from 0 to about 2;

[0062] m is an integer from 2 to 5, with the proviso that the sum of nand m is equal to 5;

[0063] R¹ is aryl, alkyl or alkoxy having from 1 to about 30 carbonatoms, cyano, halo, acid functional groups, such as sulfonic acid,carboxylic acid, phosphonic acid, phosphoric acid, phosphinic acid,boric acid, sulfonic acid and the derivative thereof, such as salts,esters, and the like; amino, alkylamino, dialkylamino, arylamino,hydroxy, diarylamino, alkylarylamino, or alkyl, aryl or alkoxysubstituted with one or more acid functional groups, such as sulfonicacid, carboxylic acid, phosphonic acid, phosphoric acid, phosphinicacid, boric acid, sulfonic acid and the derivative thereof, such assalts, esters, and the like; dialkylamino, arylamino, diarylamino,alkylarylamino, hydroxy, alkoxy, alkyl, and R² is the same or differentat each occurrence and is an R¹ substituent or hydrogen.

[0064] By way of example, polyanilines that are suitable for use in thepresent invention include those that are described in U.S. Pat. Nos.4,851,487, 4,904,553, 4,935,163, 4,940,517, 5,008,041, 5,095,076,5,256,730, 5,281,363, 5,378,403, 5,403,913, 5,427,715, 5,532,025,5,554,717, 5,567,356, 5,585,040, 5,658,649, 5,670,607, 5,773,568,5,863,465, 5,911,930, 5,917,693, and 6,030,550.

[0065] By way of example, polythiophenes that are suitable for use inthe present invention include those that are described in U.S. Pat. Nos.4,986,886, 5,158,707, 5,182,050, 5,204,423, 5,334,292, 5,482,655,5,691,062, 5,885,711, 6,004,483, 6,242,561, 6,248,818, and 6,333,145.

[0066] By way of example, polypyrroles that are suitable for use in thepresent invention include those that are described in U.S. Pat. Nos.4,569,734, 4,585,695, 4,617,353, 4,697,000, 4,697,001, 4,764,573,4,795,687, 4,847,115, 5,120,807, 5,202,060, 5,407,699, 5,522,981,5,532,025, 5,885,711, and WO 90/10095.

[0067] Examples of ICP's that are useful in the present inventioninclude polyacetylenes, polyanilines, polycarbazoles, polyfurans,polyisothionaphenes, polyparaphenylenes, polyparaphenylene sulfides,polyparaphenylene vinylenes, polyperinaphthalenes, polyphthalocyanines,polypyrroles, polyquinolines, andpolythiophenepolyheteroarylenevinylenes, in which the heteroarylenegroup is thiophene, furan or pyrrole, and mixtures thereof.

[0068] As mentioned above, when an ICP is a part of thecorrosion-responsive agent of the present invention, the ICP is dopedwith a corrosion-inhibiting anion. In a preferred embodiment thecorrosion-responsive agent comprises 2,5-dimercapto-1,3,4-thiadiazole,and the intrinsically conductive polymer is selected from the groupconsisting of polyaniline, polypyrrole, and polythiophene.

[0069] When it is desired to use an ICP doped with acorrosion-responsive agent (CRA) in the present invention, the ICP/CRAsalt can be prepared by any of the several methods that are well knownin the art. For example, polyaniline may be synthesized by chemicalpolymerization of the ICP-monomer, aniline, from aqueous solutions ormixed aqueous and organic solutions, or by electrochemicalpolymerization in solutions or emulsions, and then doped with the CRA.It is preferred, however, that the salt of an ICP and a CRA for use inthe present invention be produced:

[0070] (a) subjecting a liquid mixture containing a CRA to high-shearmixing to separate the corrosion-responsive agent into very fineparticles (i.e., less than about 20 microns number average particlediameter, preferably less than about 10 microns, more preferably lessthan about 2 microns. As an example, the liquid can be water and the CRAcan be DMcT. The high-shear mixing can be carried out, for example, bythe use of a high-speed bead mill, such as an Eiger mill. The use of aconventional blender, such as a Waring blender, for example, isinsufficient to provide the high-shear mixing required in the preferredembodiment of this method);

[0071] (b) adding an ICP monomer, such as aniline, for example, to themixture of fine CRA particles while subjecting the mixture to high-shearmixing;

[0072] (c) adding an oxidant, such as a chemical oxidant, as, forexample, ammonium peroxidisulfate, or the imposition of an electricalfield, to the mixture to facilitate polymerization of the ICP monomerinto an ICP, which is doped by the CRA to form the ICP/CRA salt; and

[0073] (d) recovering the ICP salt of the corrosion-responsive agent foruse in the invention. The ICP/CRA salt can be recovered from the liquidmedium by filtration, for example, or be centrifugation, sedimentation,or any other type of solid/liquid separation technique.

[0074] The method described above is notable in that no acid, other thanthe corrosion-responsive agent, is used during the production of the ICPsalt of the corrosion-responsive agent. Although it is possible to carryout the polymerization step in the presence of an acid other than thecorrosion-responsive agent (a non-corrosion-responsive agent acid, ornon-CRA acid), the presence of too much of the other acid is believed tocompete with the corrosion-responsive agent for the doping sites on theICP, with the result being that the ICP is doped predominantly with thenon-CRA acid, rather than with the corrosion-responsive agent, and theCRA is left unbound in the product and is susceptible to rapid leaching.

[0075] A preferred method of making an ICP doped with a CRA comprisespolymerizing the ICP monomer in the presence of a CRA and optionally oneor more non-CRA acids, wherein the molar ratio of total acids to the CRAis lower than 8:1. It is more preferred that the ratio of total acids toCRA is lower than 6:1 on a molar basis, even more preferred is when theratio of total acids to CRA is lower than 3:1 on a molar basis, yet morepreferred is a ratio of total acids to dopant inhibitor that is lowerthan 2:1 on a molar basis, and it is even more preferred that themixture in which the ICP monomer is polymerized is free of an acid otherthan the CRA.

[0076] Polymerizable corrosion-responsive agents are preferred for usein some embodiments of the present method and compositions. As usedherein, the terms “polymerizable corrosion-responsive agents” refer tocompounds that are capable of forming homodimers, homopolymers, and/orcopolymers with a component of the radiation curable resin under thesame conditions that are used to cure the coating formulation, butde-polymerize to release corrosion-inhibiting ions when exposed toelectrochemical conditions characteristic of oxidative corrosion on ametal surface.

[0077] Examples of such polymerizable corrosion-responsive agentsinclude mercaptothiadiazoles and dimercaptothiadiazoles. Whenmercaptothiadiazoles are exposed to radiation suitable for curing aradiation curable resin in the presence of a photoinitiator, it isbelieved that the free radicals generated by the photoinitiator areabsorbed by the mercaptothiadiazole as well as by the components of theradiation curable resin with the result that dimers ofmercaptothiadiazole are oxidatively formed at the same time that theradiation curable resin polymerizes and crosslinks. In like fashion,when dimercaptothiadiazoles are exposed to such radiation in a radiationcurable resin system, it is believed that the dimercaptothiadiazoleabsorbs free radicals and forms homodimers, homopolymers and/orcopolymers with a component of the resin system. Because the freeradicals are being absorbed by both the resin and the polymerizablecorrosion-responsive agent, it appears that the resin is more difficultto cure than the same system without the agent, when, in fact, theavailable free radicals are causing the formation of the resin matrixand also the dimers, polymers and co-polymers involving thecorrosion-responsive agent. A preferred polymerizablecorrosion-responsive agent is 2,5-dimercapto-1,3,4-thiadiazole.

[0078] It is believed that advantages of corrosion-inhibiting coatingsof the present invention that contain homodimers, homopolymers, and/orcopolymers of polymerizable corrosion-responsive agents include the factthat such dimers and polymers act as concentrated reservoirs of thecorrosion-responsive agent in a form that have very low rates of masstransfer through the coating matrix. Therefore, the polymerizablecorrosion-responsive agents provide coatings having very low spontaneousrelease rates for the corrosion-responsive agents and a high degree ofweatherability.

[0079] Like other corrosion-responsive agents, dimerized or polymerizedcorrosion-responsive agents release corrosion-inhibiting ions whenexposed to electrochemical (oxidation/reduction) conditionscharacteristic of those present on a metal surface that is undergoingoxidative corrosion. In the case of polymerized corrosion-responsiveagents, It is believed that the mechanism of release of the ions is dueto their reductive depolymerization.

[0080] In the present method, the corrosion-responsive agent isintermixed with a radiation curable resin to form a coating formulation.In preferred embodiments, the resin is a liquid at room temperature, andthe coating formulation is also a liquid at room temperature. Thecoating formulation can be applied to a metal surface to form a film ofthe coating formulation on the metal surface. The coating formulationcan then be exposed to radiation whereby the radiation curable resinforms a corrosion-resisting coating having a low spontaneous releaserate of the corrosion-responsive agent into the environment.

[0081] As used herein, the terms “radiation curable resin” include allresin formulations that can be cured by exposure to a form of radiation.When the term “cured” is used herein, it refers to the curing of theresin to form a solid coating. In one embodiment, a film of liquidcoating formulation reacts to form a durable solid coating. Most often,the curing reaction is a polymerization reaction, and the corrosionresistant coating often includes a matrix of crosslinked polymer chains.

[0082] The term “radiation”, as used herein, refers to the method bywhich energy is transferred to the radiation curable resin in thecoating formulation. Radiation curing can include energy transfer byultraviolet (UV), visible light, electron beams, X-rays, gamma rays,plasmas, infrared, and microwaves. Further information regardingradiation curing can be found in Fouassier, J-P, Photoinitiation,Photopolymerization, and Photocuring—Fundamentals and ApplicationsI,Hanser Publishers, New York (1995); and UV/EB Curing Primer: Inks,Coatings and Adhesives, Rechel, C. J. (Ed.), RadTech International NorthAmerica (Publ), (1995).

[0083] In one embodiment, the radiation curable resin is a UV curableresin.

[0084] In UV curable resin systems, it is common for the resin toinclude an oligomer, a photoinitiator, and optionally a monomericdiluent. Although many types of oligomers are useful in UV cured resinsystems, those that are preferred include epoxy acrylates anddiacrylates, urethane acrylates, polyurethane diacrylates, bisphenol Aepoxy acrylates, amine modified polyether acrylates, aromatic urethaneacrylates, polybutadiene acrylates, polyester acrylates, and mixturesthereof.

[0085] Examples of the photoinitiator for a UV curable resin systeminclude First cure (DEAP, First Chemical Co.), Irgacure 651 (DMPA)Irgacure 184 (HCAP), Irgacure 784 (Titanocene derivative), Irgacure 369(Morpholino ketone, BDMB), and Irgacure 907 (TPMK, from Ciba Geigy),Carocure 1173 (HAP), Darocure 1116 ((HAP derivative), DArocure 2959(Hydrophilic HAP), and Darocure 953 (C₁₃-HAP, from Merck), Esacure KIP(oligomeric HAP, from Fratelli Lamberti), Lucirin TPO (trimethyl benzoylphosphine oxide, from BASF), oligomeric alpha-hyroxyphenylketones,hydroxy-acetophenones, and others described in Fouassier ibid. at 148.

[0086] In a preferred embodiment, the photoinitiator comprises2-hydroxy-2-methyl-phenyl-1-[4-(1-methylvinyl)phenyl]propanone.

[0087] In some UV curable resins, a monomeric diluent can also bepresent. Examples of such monomers include dipropylene glycoldiacrylate, 1,3 butylene glycol diacrylate, ethoxylatedtrimethylolpropane triacrylate, propoxylated neopentyl glycoldiacrylate, tripropylene glycol diacrylate, trimethylolpropanetriacrylate, ditrimethylolpropane triacrylate, hexane diol diacrylate,and other monomers described in Fouassier, ibid at 149.

[0088] In a preferred embodiment, the UV-curable resin comprises aurethane acrylate oligomer/acrylate monomer blend. Examples of urethaneacrylate oligomer/acrylate monomer blends that are preferred for thepresent invention are products having the tradenames FD3007C1UV,EXGH-AAJG-CL, and EXGH-JH-CL, available from Allied PhotoChemical,Kimball, Mich.

[0089] In addition to the corrosion-responsive agent, the presentradiation curable resin can also contain other ingredients, and suchcomponents as thermal free-radical inhibitors, additives for flow, slip,mist, wetting and dispersion control, plasticizing diluents, fillers,light stabilizers, pigments and dyes, and the like.

[0090] When the present compositions are applied to a metal surface,they can be applied by any technique, many of which are known in theart. Examples of application techniques include dip and wipe, curtaincoating, roll coating, silk screen printing (screen printing), printingpress, lithography, offset printing, nitrogen assisted airless spraying,brushing, flowing, pouring, or the like. Screen printing is a preferredmethod of applying the coating formulation to a metal surface whenprecise control of the coating thickness is desirable.

[0091] When the present coating formulations are applied to metalsurfaces by screen printing, the metal can be coated in any screenprinting apparatus and then cured in any UV curing machine. An exampleof a suitable UV curing machine is a Switchback UV curing system,available from M&R Printing Equipment, Inc., Glen Ellyn, Ill. When afilm of the present coating formulation having as a radiation curableresin a urethane acrylate oligomer/acrylate monomer blend, such asFD3007C1UV, available from Allied PhotoChemical, Kimball, Mich., isapplied to a metal surface, the film can be cured by exposure toradiation from an iron-doped UV lamp, having peak illumination at about390 nm, with a power setting of 200 watts/inch and a belt speed of 10feet per minute (fpm) to provide an illumination exposure to the film ofthe coating formulation of about 1.4 Joules/cm². When the coatingformulation contains a polymerizable corrosion-responsive agent, such asDMcT, this combination of settings is suitable to cure a film of about10 microns thickness. When non-polymerizable corrosion-responsive agentsare used, thicker coatings, or faster belt speeds can be used.

[0092] When a film of the coating formulation is applied to a metalsurface, the thickness of the film and the amount ofcorrosion-responsive agent in the coating formulation can be selected sothat the amount of the corrosion-responsive agent is sufficient toprovide a corrosion-protective level of the agent in the cured coatingwithout interfering with the radiation curing of the resin in the film.

[0093] The corrosion-responsive agent can be present in the curedcoatings of the present invention in any amount, but it is normal forthe coating to contain the corrosion-responsive agent in an amountbetween 1% and 40% by weight. In a preferred embodiment, thecorrosion-resisting coating comprises the corrosion-responsive agent inan amount between 2% and 25% by weight, and an amount between 3% and 10%by weight is even more preferred.

[0094] The cured corrosion-inhibiting coating of the present inventioncan have any thickness, but a thickness between about 5 and about 200microns is normal. In preferred embodiments, the corrosion-inhibitingcoating has a thickness between about 10 and about 100 microns, morepreferred is a thickness between about 20 and about 60 microns, and yetmore preferred is a thickness between about 25 and about 40 microns.

[0095] Also included in the present invention are anti-corrosion coatingformulations. The present coating formulations comprise a radiationcurable resin and a corrosion-responsive agent that is capable ofreleasing a corrosion-inhibiting ion in response to exposure toelectrochemical (oxidation/reduction) conditions that are characteristicof those present on a metal surface undergoing oxidative corrosion. Thecorrosion-responsive agent of the formulation can be any one of thecorrosion-responsive agents that are described above. Likewise, theradiation curable resin can be selected from any of the radiationcurable resins that are described herein.

[0096] In a preferred coating formulation, the corrosion-responsiveagent is 2,5-dimercapto-1,3,4-thiadiazole and the radiation curableresin comprises a urethane acrylate oligomer/acrylate monomer blend.

[0097] In an embodiment of the present coating formulation, at least aportion of the corrosion-responsive agent is a polymerizablecorrosion-responsive agent.

[0098] The scope of the present invention also includes corrosionresisting coatings that are produced by curing the coating formulationsthat are described above. The corrosion resisting coatings comprise acorrosion-responsive agent dispersed in a radiation cured crosslinkedpolymer matrix. In some embodiments, at least a portion of thecorrosion-responsive agent is present in the form of a homodimer orhomopolymer of the corrosion-responsive agent, or as a copolymer withthe radiation curable resin, and wherein the portion of thecorrosion-responsive agent which is present in the form of a homodimeror homopolymer of the corrosion-responsive agent, or as a copolymer withthe radiation curable resin is capable of de-polymerizing in response toexposure to electrochemical conditions characteristic of those presenton a metal surface undergoing oxidative corrosion.

[0099] The present invention also includes metal surfaces that have beentreated by the novel method. The metal surface that is protected againstcorrosion comprises a metal surface to which is adhered aradiation-cured polymer matrix that has been formed according to any oneof the methods described herein.

[0100] It is believed that the present methods can be used to prevent orreduce corrosion for any corrodible metal. The methods and compositionsare particularly useful on steel and aluminum alloys, and moreparticularly on aluminum/copper alloys. In preferred embodiments, thealuminum/copper alloys are those that comprise at least 1% by weightcopper, more preferred are aluminum/copper alloys that contain at least4% by weight copper, yet more preferred are copper-containing aluminumalloys AA2024 and AA7075.

[0101] The following examples describe preferred embodiments of theinvention. Other embodiments within the scope of the claims herein willbe apparent to one skilled in the art from consideration of thespecification or practice of the invention as disclosed herein. It isintended that the specification, together with the examples, beconsidered to be exemplary only, with the scope and spirit of theinvention being indicated by the claims which follow the examples. Inthe examples all percentages are given on a weight basis unlessotherwise indicated.

EXAMPLE 1

[0102] This illustrates the production ofpoly(2,5-dimercapto-1,3,4-thiadiazole).

[0103] 2,5-dimercapto-1,3,4-thiadiazole (25 grams, DMcT, available fromSigma-Aldrich, Milwaukee, Wis.) was added to 50/50 deionizedwater/methanol (1500 ml). Sodium hydroxide (6.66 grams) was then addedto the mixture with stirring until the mixture became a cleartransparent yellow. The mixture was heated to about 45° C. withstirring. In a separate flask, iodine (42.13 grams) was dissolved inmethanol (400 ml) transferred to an addition funnel that is attached tothe round-bottom flask holding the DMcT mixture. The iodine solution wasadded dropwise to the DMcT mixture in the flask with stirring over aperiod of about 30 minutes. A precipitate formed immediately and wasinitially white, but became reddish brown as the iodine solution wasadded. After stirring for 2 hours, the product was recovered byfiltration, and the product was washed with acetonitrile, methanol anddeionized water. The solid product was dried at 70° C. until dry.Product was a light yellow solid.

EXAMPLE 2

[0104] This illustrates the production of polyaniline doped with(2,5-dimercapto-1,3,4-thiadiazole).

[0105] Synthesis of DMcT-Salt of Polyaniline (Blender Method):

[0106] 2,5-dimercapto-1,3,4-thiadiazole (93 grams) was ground in amortar with a pestle to a fine powder. The powder was added to deionizedwater in a Waring blender and emulsified in the blender for 1 minute.Aniline (57 grams) was added to the mixture in the blender andemulsified for 1 minute. The mixture in the blender was transferred to a3 liter round-bottom jacketed flask that was cooled to about 5° C. andblanketed with nitrogen. Ammonium peroxidisulfate (170 grams, APDS) wasdissolved in deionized water and transferred to an addition funnel,which was attached to the round-bottom flask. The APDS solution was thenadded dropwise to the mixture in the flask over a period of about 15minutes while maintaining the temperature of the mixture in the flaskbelow about 5° C. The mixture was stirred for 3 hours at about 5° C.under a nitrogen blanket. The product was recovered by filtration, andthe solid product was washed with deionized water.

[0107] Synthesis of DMcT-Salt of Polyaniline (Eiger Mill Method):

[0108] The following materials were added to an Eiger mill (Model Mini100 Motormill, Eiger Machinery, Inc., Grayslake, Ill.): glass beads (60ml), deionized water (325 ml), 2,5-dimercapto-1,3,4-thiadiazole (25 g,DMcT, CAS No. 1072-71-5). The charge was milled at 5000 rpm for about 15minutes to produce a fine yellow slurry. Then aniline (15.32 g) wasadded dropwise over about 18 to 40 minutes, while the mill was operatedat a speed of 5000 rpm. The mixture in the mill was milled an additionaltime period (up to 45 minutes) and then discharged from the mill.

[0109] The above procedure was repeated twice more and the threeproducts of the procedure were combined and added to a 3 liter jacketedround-bottomed flask with an overhead stirrer. To the salt mixture wasadded dropwise 138 g ammonium peroxidisulfate (APS) in water at 2° C.The reaction exotherm of 13° C. was noted 77 minutes after the beginningof the APS addition. The dark-green-black slurry was stirred overnightat 2° C.

[0110] The slurry of fine particles was filtered, washed three timeswith 1000 ml deionized water, air dried, and then dried in a vacuum ovento give the product powder. The particles size by light microscopicexamination was estimated to be less than about 20 microns.

[0111] Chromatographic Characterization of Poly-DMcT and the DMcT-Saltof Polyaniline:

[0112] A sample of poly-DMcT, produced as described in Example 1, andtwo samples of the DMcT-salt of polyaniline (Pani-DMcT), producedseparately by the first method described above, were characterized bysize-exclusion chromatography (SEC) by methods described by Kinlen etal., in Macromolecules, 31:1735-1744 (1998). Polymer solutions used inthe analysis were prepared in the SEC mobile phase (N-methylpyrrolidone(NMP) saturated with ammonium formate) at a nominal polymerconcentration of 5 mg/ml. In the case of poly-DMcT and the two Pani-DMcTsamples, only partial solubility was found. The solutions werecentrifuged in a laboratory microcentrifuge at 8,000 rpm for 2 minutes.All insolubles sedimented under these conditions and only the solublefractions were employed in the SEC analysis. The chromatographic flowrate was 0.4 ml/min and an injection volume of 400 microliters was used.

[0113] As shown in FIG. 1, the differential refractive index (DRI)chromatograms for the polyaniline standard (Sigma-Aldrich Co., St.Louis, Mo.) and the soluble fraction of poly-DMcT are distinctlydifferent. The later retention time for the poly-DMcT is consistent witha low molecular weight polymer resulting from partial solubility(extraction) of the solid poly-DMcT in the SEC solvent.

[0114] Overlaying the DRI curves for the two homopolymer standards inFIG. 1, with the corresponding curves for the Pani-DMcT samples labeled#1 and #2, produced the data shown in FIG. 2. The chromatograms ofPani-DMcT #1 and #2 strongly indicate the presence of poly-DMcT, as wellas the presence of polyaniline. Components eluting with retention timesearlier than the polyaniline standard suggest multiple species, possiblypure polyaniline and copolymers of aniline and DMcT.

[0115] The strong indication of poly-DMcT in Pani-DMcT samples #1 and #2is clearly demonstrated in FIG. 3, which is a retention time expansionof the polymer region of the SEC chromatograms. By contrast, a similarexpansion, shown in FIG. 4, reveals that Pani-DMcT #1 contains lesspoly-DMcT relative to its earlier eluting components than in the case ofPani-DMcT #2.

[0116] This data shows that polyaniline that is polymerized in thepresence of DMcT provides a product having both polyaniline andpoly-DMcT. The product may also have some types of DMcT dimers andoligomers, and even some types of co-polymers involving DMcT andaniline. These structures are believed to be important in providing thepresent cured coatings with the advantages of a low spontaneous releaserate for the corrosion-inhibiting DMcT anion, while also providing acoating with a significant concentration of the corrosion-responsiveagent.

EXAMPLE 3

[0117] This illustrates the production of UV-curable coatingformulations containing (2,5-dimercapto-1,3,4-thiadiazole),poly(2,5-dimercapto-1,3,4-thiadiazole), and polyaniline doped with(2,5-dimercapto-1,3,4-thiadiazole).

[0118] A measured amount of a UV-curable resin (160 g; available asFD3007CI UV, from Allied PhotoChemical, Kimball, Mich.) was charged toan Eiger Mini Mill (Model 100 VSE; Eiger Machinery, Inc., Grayslake,Ill.), and an amount (17.78 g dry weight) of a corrosion-responsiveagent, selected from 2,5-dimercapto-1,3,4-thiadiazole (DMcT),poly(2,5-dimercapto-1,3,4-thiadiazole), and polyaniline doped with(2,5-dimercapto-1,3,4-thiadiazole) (Pani-DMcT) was added as a solidmaterial to the liquid to give a mixture that was 10% by weightcorrosion-responsive agent. The solids and the liquid were milled untilthe solids were of the desired particle size and were well-dispersed inthe liquid.

[0119] A known weight (100 g) of the 10% w/w mixture was drawn from themill, and 77.78 g of the UV-curable resin was added to the mixtureremaining in the mill to make a mixture that was 5% by weight DMcT, andthe mixture in the mill was milled until the solids were well dispersed.

[0120] The 10% mixture and the 5% mixtures were then ready for use inthe coating formulations of the invention. The relative amounts ofUV-curable resin and corrosion-responsive agent can be varied to providea coating formulation having any desirable concentration of thecorrosion-responsive agent.

[0121] This method could be used with any radiation curable resin andany corrosion-responsive agent to prepare a UV-curable coatingformulation of the present invention.

EXAMPLE 4

[0122] This illustrates the application of UV-cured coatings containing2,5-dimercapto-1,3,4-thiadiazole,poly(2,5-dimercapto-1,3,4-thiadiazole), and polyaniline doped with(2,5-dimercapto-1,3,4-thiadiazole) to aluminum panels.

[0123] Coating formulations comprising a UV-curable resin (available asEXGH-JH-CL from Allied PhotoChemical Co.) containing 0%, 5%, and 10% w/wof either 2,5-dimercapto-1,3,4-thiadiazole,poly(2,5-dimercapto-1,3,4-thiadiazole), or polyaniline doped with(2,5-dimercapto-1,3,4-thiadiazole were applied onto one surface of 3″×6″aluminum panels selected from 2024 aluminum alloy, 2024 aluminum alloycleaned by scrubbing with Scotch Brite®, or 7076 aluminum alloy to formthe samples shown in Table 1. Each coating formulation was applied byscreen printing in a Coleman press through a 305 mesh screen or a 380mesh screen with an 80 dur. Squeegee. After the application of a film ofthe coating formulation had been applied to a panel, the coating filmwas cured by passage of the coated panel through an M&R Switchback UVcuring system (Model CWBK-60-208-1-60, available from M&R Equipment Co.,Glen Ellyn, Ill.) using a belt speed of 10 fpm and an intensity settingof 200 watts/in. (1.123 watts/cm²) for an iron-doped lamp, to provide apower input of 1.346 Joules/cm² to the coated surface for each curingpass. Radiation power and exposure was measured with a High Energy UVRadiometer (available under the tradename UVICURE® Plus from EIT Inc.,Sterling, Va.).

[0124] For each coating, a total of three coating/curing cycles wascarried out. Coating weight and the thickness of the cured coating areshown in Table 1. Also shown in Table 1 is the coating density.

[0125] The cured coatings produced by this method had a final thicknessof about 30-35 microns and a density of from about 0.005 to 0.006lbs/mil/ft². TABLE 1 Aluminum alloy samples with UV-curedcorrosion-responsive coatings. Weight Before Weight Dry Film CoatingBelt After Coating Thickness lbs/mil/ Substrate^(a) (Gms) Coating^(b)Mesh^(c) Passes^(c) Speed^(c) Watts/inch^(d) Joules^(e) Coating Weight(Microns) ft2 2024-T3 CC 25.81 10% DMcT 305 3 10 1.164 1.398 26.17 0.3635 0.0058 2024-T3 CC 25.9 10% DMcT 305 3 10 1.164 1.398 26.28 0.38 350.0062 2024-T3 CC 25.44 10% DMcT 305 3 10 1.164 1.398 25.81 0.37 340.0062 2024-T3 CC 25.46 10% DMcT 305 3 10 1.164 1.398 25.83 0.37 340.0062 2024-T3 CC 25.73 10% PolyDMcT 305 3 10 1.164 1.398 26.07 0.34 350.0055 2024-T3 CC 25.44 10% PolyDMcT 305 3 10 1.164 1.398 25.8 0.36 340.0060 2024-T3 CC 25.73 10% PolyDMcT 305 3 10 1.164 1.398 26.08 0.35 360.0055 2024-T3 CC 25.71 10% PolyDMcT 305 3 10 1.164 1.398 26.05 0.34 350.0055 2024-T3 CC 25.77 10% PANI-DMcT 380 3 10 1.164 1.398 26.02 0.25 260.0055 2024-T3 CC 25.69 10% PANI-DMcT 380 3 10 1.164 1.398 25.96 0.27 280.0055 2024-T3 CC 25.58 10% PANI-DMcT 380 3 10 1.164 1.398 25.83 0.25 270.0053 2024-T3 CC 25.67 10% PANI-DMcT 380 3 10 1.164 1.398 25.93 0.26 270.0055 2024-T3 CC 25.7 Allied Clear 305 3 10 1.164 1.398 26.01 0.31 330.0053 2024-T3 CC 25.74 Allied Clear 305 3 10 1.164 1.398 26.05 0.31 320.0055 2024-T3 Scotch Brite 25.81 10% DMcT 305 3 10 1.164 1.398 26.180.37 35 0.0060 2024-T3 Scotch Brite 25.79 10% DMcT 305 3 10 1.164 1.39826.16 0.37 35 0.0060 2024-T3 Scotch Brite 25.8 10% DMcT 305 3 10 1.1641.398 26.17 0.37 35 0.0060 2024-T3 Scotch Brite 25.88 10% DMcT 305 3 101.164 1.398 26.25 0.37 n/a n/a 2024-T3 Scotch Brite 25.76 10% PolyDMcT305 3 10 1.164 1.398 26.12 0.36 34 0.0060 2024-T3 Scotch Brite 25.52 10%PolyDMcT 305 3 10 1.164 1.398 25.87 0.35 34 0.0059 2024-T3 Scotch Brite25.87 10% PolyDMcT 305 3 10 1.164 1.398 26.22 0.35 34 0.0059 2024-T3Scotch Brite 25.78 10% PolyDMcT 305 3 10 1.164 1.398 26.16 0.38 n/a n/a2024-T3 Scotch Brite 25.8 10% PANI-DMcT 380 3 10 1.164 1.398 26.05 0.2526 0.0055 2024-T3 Scotch Brite 25.79 10% PANI-DMcT 380 3 10 1.164 1.39826.04 0.25 26 0.0055 2024-T3 Scotch Brite 25.68 10% PANI-DMcT 380 3 101.164 1.398 25.96 0.28 27 0.0059 2024-T3 Scotch Brite 25.71 10%PANI-DMcT 380 3 10 1.164 1.398 25.98 0.27 n/a n/a 2024-T3 Scotch Brite25.79 Allied Clear 305 3 10 1.164 1.398 26.12 0.33 38 0.0049 2024-T3Scotch Brite 25.79 Allied Clear 305 3 10 1.164 1.398 26.1 0.31 n/a n/a7075-T6 CC 26.11 10% DMcT 305 3 10 1.164 1.398 26.46 0.35 34 0.00597075-T6 CC 25.96 10% DMcT 305 3 10 1.164 1.398 26.33 0.37 33 0.00647075-T6 CC 26.09 10% DMcT 305 3 10 1.164 1.398 26.46 0.37 37 0.00577075-T6 CC 26.13 10% DMcT 305 3 10 1.164 1.398 26.49 0.36 36 0.00577075-T6 CC 26.16 10% PolyDMcT 305 3 10 1.164 1.398 26.53 0.37 36 0.00587075-T6 CC 26.13 10% PolyDMcT 305 3 10 1.164 1.398 26.5 0.37 34 0.00627075-T6 CC 26.18 10% PolyDMcT 305 3 10 1.164 1.398 26.53 0.35 33 0.00607075-T6 CC 26.18 10% PolyDMcT 305 3 10 1.164 1.398 26.53 0.35 33 0.00607075-T6 CC 26.18 10% PANI-DMcT 380 3 10 1.164 1.398 26.43 0.25 28 0.00517075-T6 CC 26.12 10% PANI-DMcT 380 3 10 1.164 1.398 26.39 0.27 26 0.00597075-T6 CC 26.02 10% PANI-DMcT 380 3 10 1.164 1.398 26.27 0.25 25 0.00577075-T6 CC 26.13 10% PANI-DMcT 380 3 10 1.164 1.398 26.39 0.26 25 0.00597075-T6 CC 26.13 Allied Clear 305 3 10 1.164 1.398 26.46 0.33 31 0.00617075-T6 CC 26.12 Allied Clear 305 3 10 1.164 1.398 26.43 0.31 31 0.0057

EXAMPLE 5

[0126] This illustrates the anti-corrosion performance of aluminumpanels coated with UV-cured coatings containing(2,5-dimercapto-1,3,4-thiadiazole),poly(2,5-dimercapto-1,3,4-thiadiazole), and polyaniline doped with(2,5-dimercapto-1,3,4-thiadiazole) in salt-fog tests.

[0127] Samples of aluminum alloy (3″×6″×0.032″ bare 2024 T3 aluminumalloy) were pretreated with a chromate conversion coating according toMilitary Specification MIL-C-5541/PS13209, and then coated with thecoatings described in Table 2 and subjected to salt/fog exposure testingaccording to ASTM B-117 test protocol. Each test panel was scribed toproduce a scratch that penetrated the coating and uncovered the barealuminum alloy. Table 2 shows the performance of the samples after 1,560hours of salt/fog exposure. It can be seen that all test panels havingeither polyaniline/DMcT or DMcT corrosion-responsive agents ascomponents of the coatings were significantly protected againstcorrosion. TABLE 2 Salt/fog testing of aluminum alloy coated withcoatings containing corrosion-responsive agents. NO. OF DRY FILMCORROSION PANEL COATING COATING DRY THICKNESS PERFORMANCE NO. TYPEMETHOD PASSES (microns) AT 1560 HOURS 8C 7.5% #10 Wire 2 32 Singleblister PANI/DMcT draw bar growing in IN EXGH- circumference AAJG-CL 9CSame Same 2 35 No change 1C Same Same 2 32 Blister next to scratchgrowing 8D 7.5% ATM 3 32 No change PANI/DMcT screen in EXGH-JH- printingCL 9D Same Same 3 33 Blister next to scratch growing 10D Same Same 3 32Blister next to scratch growing 8E 7.5% DMcT #10 Wire 2 31 No change INEXGH- draw bar AAJG-CL 9E Same Same 2 34 No change 10E Same Same 2 30 Nochange 8F 7.5% ATM 3 33 No change PANI/DMcT screen in EXGH-JH- printingCL 9F Same Same 3 32 No change 10F Same Same 3 33 No change

[0128] All references cited in this specification, including withoutlimitation all papers, publications, patents, patent applications,presentations, texts, reports, manuscripts, brochures, books, internetpostings, journal articles, periodicals, and the like, are herebyincorporated by reference into this specification in their entireties.The discussion of the references herein is intended merely to summarizethe assertions made by their authors and no admission is made that anyreference constitutes prior art. Applicants reserve the right tochallenge the accuracy and pertinency of the cited references.

[0129] In view of the above, it will be seen that the several advantagesof the invention are achieved and other advantageous results obtained.

[0130] As various changes could be made in the above methods andcompositions without departing from the scope of the invention, it isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:
 1. A method of protecting a metal surface againstcorrosion, the method comprising: applying to the metal surface acoating formulation that comprises a radiation curable resin and acorrosion-responsive agent that is capable of releasing acorrosion-inhibiting ion in response to exposure to electrochemicalconditions characteristic of those present on a metal surface undergoingoxidative corrosion; and exposing the coating formulation to radiationwhereby the radiation curable resin forms a corrosion-resisting coatinghaving a low spontaneous release rate of the corrosion-responsive agentinto the environment.
 2. The method according to claim 1, wherein thecoating formulation is applied to the metal surface as a film andwherein the thickness of the film and the amount of thecorrosion-responsive agent in the formulation are selected so that theamount of the corrosion-responsive agent is sufficient to provide acorrosion-protective level of the agent in the cured coating withoutinterfering with the radiation curing of the resin in the film.
 3. Themethod according to claim 1, wherein the corrosion-inhibiting ion is acorrosion-inhibiting cation.
 4. The method according to claim 3, whereinthe corrosion-inhibiting cation is an inorganic cation.
 5. The methodaccording to claim 4, wherein the inorganic corrosion-inhibiting cationis selected from the group consisting of: Ca, Sr, Ti, Mo, Zr, Ce, andFe.
 6. The method according to claim 3, wherein the corrosion-inhibitingcation is an organic cation.
 7. The method according to claim 6, whereinthe organic corrosion-inhibiting cation is selected from the groupconsisting of: ammonium, alkyl-ammonium, and cycloalkyl-ammonium.
 8. Themethod according to claim 1, wherein the corrosion-inhibiting ion is acorrosion-inhibiting anion.
 9. The method according to claim 8, whereinthe corrosion-inhibiting anion is an inorganic anion.
 10. The methodaccording to claim 9, wherein the inorganic corrosion-inhibiting anionis selected from the group consisting of: CrO₄ ²⁻, CrO₁₂H₈ ⁵⁻, PO₄ ³⁻,HPO₄ ³⁻, MoO₄ ²⁻, BO₂ ²⁻, SiO₃ ²⁻, NCN²⁻, HPO₃ ²⁻, NO²⁻, P₃O₁₀ ⁵⁻; andCO₃ ²⁻.
 11. The method according to claim 10, wherein the inorganiccorrosion-inhibiting anion is selected from the group consisting of: PO₄³⁻, HPO₄ ³⁻, MoO₄ ²⁻, BO₂ ²⁻, SiO₃ ²⁻, NCN²⁻, and P₃O₁₀ ⁵⁻.
 12. Themethod according to claim 8, wherein the corrosion-inhibiting anion isan organic anion.
 13. The method according to claim 12, wherein theorganic corrosion-inhibiting anion is one that is formed by theionization of a corrosion-responsive agent that is selected from thegroup consisting of mercapto-substituted organics, thio-substitutedorganics, and dimers, trimers, oligomers, and polymers thereof.
 14. Themethod according to claim 12, wherein the corrosion-inhibiting anion isone that is formed by the ionization of a corrosion-responsive agentthat is selected from the group consisting of:1-(4-hydroxyphenyl)-1H-tetrazol-5-thiol, 1,2,4-triazole-3-thiol,1-pyrollidinecarbodithioic acid, 2,2′-dithiobis(benzothiazole),2,4-dimercapto-6-amino-5-triazine, 2,4-dithiohydantoin,2,5-dimercapto-1,3,4-thiodiazole, 2,5-dimethylbenzothiazole,2-amino-1,3,4-thiadiazole, 2-mercapto-5-methylbenzimidazole,2-mercapto-5-nitrobenzimidazole, 2-mercaptobenzimidizole,2-mercaptobenzoxazole, 2-mercaptoethane sulfonic acid,2-mercaptoimidazole, 2-mercaptothiazoline, 2-thiouracil,3-amino-5-mercapto-1,2,4-triazole,5,5-dithio-bis(1,3,4-thiadiazole-2(3H)-thione,5-amino-1,3,4-thiadiazole, 6-amino-2-mercaptobenzothiazole,6-ethoxy-2-mercaptobenzothiazole, 6-mercaptopurine, -alky- orN-cycloalkyl-dithiocarbamates, alkyl- and cyclo-alkyl mercaptanes,benzothiazole, dimercapto pyridine, dimethyldithio carbamic acid,dithiocyanuric acid, mercaptobenzothiazole, mercaptobenzoxazole,mercaptoethanesulfonic acid, mercaptoimidazole, mercaptopyridine,mercaptopyrimidine, mercaptoquinoline, mercaptothiazole,mercaptothiazoline, mercaptotriazole, O,O-dialkyl- andO,O-dicycloalkyl-dithiophosphates, O-alkyl- orO-cycloalkyl-dithiocarbonates, o-ethylxanthic acid,quinoxaline-2,3-thiol, thioacetic acid, thiocresol, thiosalicylic acid,trithiocyanuric acid, and dimers, trimers, oligomers, and polymersthereof.
 15. The method according to claim 13, wherein themercapto-substituted organic comprises a mercapto-substituted aryl orheteroaryl.
 16. The method according to claim 14, wherein thecorrosion-inhibiting anion is one that is formed by the ionization of2,5-dimercapto-1,3,4-thiadiazole.
 17. The method according to claim 12,wherein the organic corrosion-inhibiting agent comprises an organicphosphonic acid, or salt or ester thereof.
 18. The method according toclaim 17, wherein the organic phosphonic acid is a anaminoalkylphosphonic acid or a hydroxyalkylphosphonic acid having thegeneral formula: R¹—(CH₂—(PO₃)M₂)_(x), orR¹—((PO₃)M₂)_(x) where: M isselected from the group consisting of hydrogen, an alkaline metal,alkyl, alkenyl, alkynyl, alkoxy, aryl, cyclic, heteroaryl, andheterocyclic; R₁ is selected from the group consisting of amino,aminoalkyl, and hydroxyalkyl; and x is a number equal to the valence ofR¹, provided that x is 1 or higher.
 19. The method according to claim18, where x is 2 or higher.
 20. The method according to claim 17,wherein the organic phosphonic acid is selected from the groupconsisting of: n-octyldecylaminobismethylenephosphonic acid,dodecyldiphosphonic acid, ethylidenediaminotetramethylenephosphonicacid, hydroxyethylidenediphosphonic acid,1-hydroxyethylidene1,1-diphosphonic acid, isopropenyldiphosphonic acid,N,N-dipropynoxymethylaminotrimethylphosphonic acid,oxyethylidenediphosphonic acid, 2-carboxyethylphosphonic acid,N,N-bis(ethynoxymethyl)aminomethyltriphosphonic acid,nitriletrimethylenephosphonic acid, aminotrimethylenephosphonic acid,diethylenetriaminepentakis(methylenephosphonic) acid,amino(trimethylenephosphonic acid), nitrilotris(methylenephosphonicacid), ethylenediaminotetra(methylenephosphonic acid),hexamethylenediaminetetra(methylenephosphonic acid),diethylenetriaminepenta(methlenephosphonic acid), glycine,N,N-bis(methylenephosphonic acid),bis(hexamethylenetriaminepenta(methylenephosphonic acid), and2-ethylhexylphosphonic acid.
 21. The method according to claim 17,wherein the organic phosphonic acid is selected from the groupconsisting of: alkali metal ethane 1-hydroxy diphosphonates (HEDP),alkylene poly(alkylene phosphonate), and amino phosphonate compounds.22. The method according to claim 21, wherein the organic phosphonicacid is selected from the group consisting of: amino aminotri(methylenephosphonic acid) (ATMP), nitrilo trimethylene phosphonates (NTP),ethylene diamine tetra methylene phosphonates, diethylene triamine pentamethylene phosphonates (DTPMP), ethane 1-hydroxy diphosphonate (HEDP),and salts or esters thereof.
 23. The method according to claim 1,wherein the corrosion-responsive agent is the salt of an intrinsicallyconductive polymer and a corrosion-inhibiting anion that is selectedfrom the corrosion-inhibiting anions described in any one of claims9-22.
 24. The method according to claim 23, wherein the intrinsicallyconductive polymer is selected from the group consisting ofpolyacetylene, polyaniline, polycarbazole, polyfuran,polyheteroarylenevinylene, in which the heteroarylene group isthiophene, furan or pyrrole, polyisothionaphene, polyparaphenylene,polyparaphenylene sulfide, polyparaphenylene vinylene,polyperinaphthalene, polyphthalocyanine, polypyrrole, polyquinoline,polythiophene, and mixtures thereof.
 25. The method according to claim24, wherein the corrosion-responsive agent comprises2,5-dimercapto-1,3,4-thiadiazole, and the intrinsically conductivepolymer is selected from the group consisting of polyaniline,polypyrrole, and polythiophene.
 26. The method according to claim 1,wherein the corrosion-responsive gent is a polymerizablecorrosion-responsive agent.
 27. The method according to claim 1, whereinthe radiation curable resin is a UV-curable resin.
 28. The methodaccording to claim 27, wherein the UV-curable resin comprises anoligomer, a photoinitiator, and optionally a monomeric diluent.
 29. Themethod according to claim 28, wherein the oligomer comprises a compoundselected from the group consisting of bisphenol A epoxy acrylates, aminemodified polyether acrylates, aromatic urethane acrylates, polyesteracrylates, and mixtures thereof.
 30. The method according to claim 28,wherein the photoinitiator comprises a compound that is selected fromthe group consisting of oligomeric alpha-hyroxyphenylketones, andhydroxy-acetophenones.
 31. The method according to claim 30, wherein thephotoinitiator comprises2-hydroxy-2-methyl-phenyl-1-[4-(1-methylvinyl)phenyl]propanone.
 32. Themethod according to claim 28, wherein the optional monomeric diluent ispresent and is selected from the group consisting of dipropylene glycoldiacrylate, 1,3 butylene glycol diacrylate, ethoxylatedtrimethylolpropane triacrylate, propoxylated neopentyl glycoldiacrylate, tripropylene glycol diacrylate, trimethylolpropanetriacrylate, ditrimethylolpropane triacrylate, and hexane dioldiacrylate.
 33. The method according to claim 28, wherein the UV-curableresin comprises a urethane acrylate oligomer/acrylate monomer blend. 34.The method according to claim 1, wherein the step of applying thecoating formulation comprises screen printing.
 35. The method accordingto claim 1, wherein the corrosion-resisting coating comprises thecorrosion-responsive agent in an amount between 1% and 40% by weight.36. The method according to claim 35, wherein the corrosion-resistingcoating comprises the corrosion-responsive agent in an amount between 2%and 25% by weight.
 37. The method according to claim 36, wherein thecorrosion-resisting coating comprises the corrosion-responsive agent inan amount between 3% and 10% by weight.
 38. The method according toclaim 1, wherein the exposure of the coating formulation to radiationcomprises exposure to a type of radiation selected from the groupconsisting of UV radiation, electron beam, X-rays, gamma rays,microwaves, laser light, and visible light.
 39. An anti-corrosioncoating formulation comprising a radiation curable resin and acorrosion-responsive agent that is capable of releasing acorrosion-inhibiting ion in response to exposure to electrochemicalconditions characteristic of those present on a metal surface undergoingoxidative corrosion.
 40. The formulation according to claim 39, whereinthe corrosion-responsive agent is one that is selected from thosedescribed in any one of claims 3-26, and the radiation curable resin isone that is selected from those described in any one of claims 27-33.41. The formulation according to claim 39, wherein thecorrosion-responsive agent is 2,5-dimercapto-1,3,4-thiadiazole and theradiation curable resin comprises a urethane acrylate oligomer/acrylatemonomer blend.
 42. The formulation according to claim 39, wherein atleast a portion of the corrosion-responsive agent is a polymerizablecorrosion-responsive agent.
 43. A corrosion resisting coating for ametal surface, the coating comprising a corrosion-responsive agentdispersed in a radiation cured crosslinked polymer matrix.
 44. Thecoating according to claim 43, wherein at least a portion of thecorrosion-responsive agent is present in the form of a homodimer orhomopolymer of the corrosion-responsive agent, or as a copolymer withthe radiation curable resin, and wherein the portion of thecorrosion-responsive agent which is present in the form of a homodimeror homopolymer of the corrosion-responsive agent, or as a copolymer withthe radiation curable resin is capable of de-polymerizing in response toexposure to electrochemical conditions characteristic of those presenton a metal surface undergoing oxidative corrosion.
 45. A metal surfaceprotected against corrosion comprising: a metal surface; to which isadhered, a radiation-cured polymer matrix that has been formed accordingto claim
 1. 46. A method of producing an intrinsically conductivepolymer salt of a corrosion-responsive agent, the method comprising: (a)subjecting a liquid mixture containing a corrosion-responsive agent tohigh-shear mixing to separate the corrosion-responsive agent into veryfine particles; (b) adding a monomer of an intrinsically conductivepolymer to the mixture of fine corrosion-responsive agent particleswhile subjecting the mixture to high-shear mixing; (c) adding an oxidantto the mixture to facilitate polymerization of the monomer of theintrinsically conductive polymer into an intrinsically conductivepolymer which is doped by the corrosion-responsive agent to form theICP/CRA salt; and (d) recovering the ICP/CRA salt.
 47. The methodaccording to claim 46, wherein the polymerization of the monomer of theintrinsically conductive polymer is carried out in the presence of acorrosion-responsive agent and an acid that is not acorrosion-responsive agent, wherein the molar ratio of total acids tocorrosion-responsive agent is lower than 8:1.
 48. The method accordingto claim 47, wherein the molar ratio of total acids tocorrosion-responsive agent is lower than 2:1.
 49. The method accordingto claim 47, wherein the polymerization is carried out in a medium thatis free of an acid other than the corrosion-responsive agent.